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On the web some info is good some is snake oil. My soil is so alkali if vinegar is poured on it, it foams. Washed all ash out of some charcoal from the woodstove and soaked it in vinegar until it was slightly acidic then soaked in fish emulsion and mixed with compost. There seemed to be no change in production from the bed it was used on last year. I still have hope for 2015.

The stuff needs to age for at least a year and you see critters in it before you put it in the garden.
Then it needs to have 1000 year old pot shards mixed in with it made by people we dont even know how they were.
The best information I have on it is from a book called 1491 about pre Columbian history.
No snake oil.
If you have good soil it isn't going to make it that much better it is for improving bad soil.
One thing to remember is the reason they call potash what they do is because it was derived from burning potted plants.

Bio char can be made from different types of wood each wood has different results. The temperature at which the Bio char is made (basically the amount of oxygen that fuels the fire) determines the amount of ash residue left inside of the Bio char.

Bio char can be made from different types of wood each wood has different results. The temperature at which the Bio char is made (basically the amount of oxygen that fuels the fire) determines the amount of ash residue left inside of the Bio char.

That makes sense they used different woods to make various gunpowder years ago.
I used to haul hardwood to a place that stacked in huge concrete kilns and they would burn it in a low oxygen environment.
They would then haul the charcoal to another plant to make charcoal bricketts.

At a talk about biochar, it was explained that it should be made at high heat. The way it works is to provide habitat for beneficial bacteria, and it didn't work without compost being added at the same time. Regular charred wood doesn't cut it. The biochar does not break down even after 1000's of years. The biochar + compost combination added to urban fill produced astounding results. Plants grew tremendously instead of being stunted as usual in that environment. Too bad we can't make the stuff in the city. We have plenty to burn, but I doubt the fire department would go for it.